methanogen

A methanogen is a microorganism that produces methane as a by-product
of its metabolism. All known methanogens are both archaeans and obligate anaerobes, that is, they cannot
live in the presence of oxygen. They are commonly found in wetlands, where
they generate methane in the form of marsh gas, and in the guts of animals
such as ruminants and humans, where they are responsible for flatulence.

Some methanogens, described as hydrotropic, use carbon dioxide as a source
of carbon and hydrogen as a source of energy. Some of the carbon dioxide
reacts with, and is reduced by, hydrogen to produce methane. The methane
is turn gives rise to a proton motive force across a membrane, which is
used to generate ATP – a key source of
cellular energy. Other methanogens, called acetotrophic, use acetate (CH3COO-)
as a source of both carbon and energy. Still other methanogens exploit methylated
compounds such as methylamines, methanol, and methanethiol as well.

More than 50 species of methanogens have been identified, including a number
that are extremophiles. Live methanogens
were recovered from a core sample taken from 3 kilometers under Greenland
by researchers from the University of California, Berkeley. Another study
discovered methanogens in soil and vapor samples from the vicinity of the
Mars Desert Research Station in Utah. These findings add weigh to speculation
by some scientists that methanogens may be responsible for the methane that
has been in detected in the atmosphere of
Mars.